In order to increase the degree of integration of semiconductor memory elements, development of novel techniques in production steps has been demanded. When a MOS structure is utilized in semiconductor memory elements, highly integrated semiconductor memory elements such as DRAM of approximately 4 giga, a gap between the source electrode and the drain electrode becomes as small as approximately 0.13 μm. Therefore, it is predicted that switching by gate voltage which has been conventionally utilized as an operation principle of MOS elements is disabled. Hence, small gap between the source electrode and the drain electrode causes malfunctions of the elements may be caused due to phenomena of tunneling through the gate oxide film, and of tunneling between the source electrode and the drain electrode even in the state without applying the gate voltage. Therefore, for manufacture of giga-order or tera-order devices, it is necessary to use modes other than those currently used on the basis of the MOS structure.
As one of the elements of such novel modes, single electron semiconductor elements (also referred to as “Single Electron Transistor”, hereinafter, abbreviated as SET) in which a single electron tunnel effect is utilized have been focusing attention.
SET is an element which works on the basis of a phenomenon referred to as coulomb blockade. More specifically, elements that operate depending on alteration of electrostatic energy generated upon tunneling of one electron as a unit between fine conductors which can be charged or discharged are referred to as single electron element. Operation of the same has been confirmed in the form of single electron memories, single electron transistors and the like. Junctions which can result in observation of such a coulomb blockade phenomenon are referred to as fine tunnel junctions.
In conventional SET, fine tunnel junctions have been formed by fine patterning with electron beam lithography (for example, see Nonpatent Document 1 (T. A. Fulton and G. J. Dolan: “Observation of Single-Electron Charging Effects in Small Tunnel Junctions”, Phys. Rev. Lett. Vol. 59, No. 1, pp. 109-112 (1987).), however, capacity of the fine tunnel junction which is formable thereby can not make small enough, therefore, operation of SET at a room temperature was difficult. As a matter of fact, for enabling the observation of such a phenomenon referred to as coulomb blockade as described above at a room temperature, alteration of the electrostatic energy should be significantly large as compared with the alteration of thermal energy.
To this end, size of the conductor which can be charged or discharged should be equal to or less than 20 nm, in addition, intervals provided by arranging these conductor which can be charged or discharged should be equal to or less than several nanometers. Such a minute fine tunnel junction can be hardly produced by a pattern formation method according to currently employed lithographic technique. Alternatively, even if it can be produced, production of large quantity in a high yield is extremely difficult.
As a method for production of the SET structural device by arranging nano particles between fine electrodes formed on a substrate, Nonpatent Document 2 (A. Dutta et al.,: “Single-Electron Tunneling Devices Based on Silicon Quantum Dots Fabricated by Plasma Processes”, Jpn. J. Appl. Phys. Vol. 39, pp. 264-267 (2000).) discloses a method in which Si nano particles are fixed on a substrate on which fine electrodes (source electrode and drain electrode) are provided, and an Si particle chain is formed in a nano gap between the source electrode and the drain electrode (hereinafter, referred to as nano gap between source/drain).
Also, Nonpatent Document 3 (T. Sato et al.,: “Sigle electron transistor using molecularly linked gold colloidal particle chain”, J. Appl. Phys. 82 (2), p 696 (1997).) discloses a method in which an Au nano particle chain is formed in the nano gap between source/drain by allowing Au nano particles to be adsorbed on a substrate on which fine electrodes (source electrode and drain electrode) are formed, then modifying the Au nano particle with dithiol, and further allowing for adsorption of the Au nano particle.